Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Current assets
Cash and cash equivalents		$ 2,870	$ 2,641	$ 4,010	$ 4,970
Short-term investments		5,444	0
Accounts and notes receivable, net		4,138	1,099
Device and accessory inventory		1,064	1,173
Prepaid expenses and other current assets		601	1,920
Total Current Assets		14,117	6,833
Investment in subsidiaries		0	0
Property, plant and equipment, net		19,209	20,297
Due from consolidated affiliate		0	0
Note receivable from consolidated affiliate		0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill		6,579	6,575	6,575
FCC licenses and other		40,585	40,073
Definite-lived intangible assets, net		3,320	4,469
Other assets		1,313	728
Total assets		85,123	78,975	82,841
Current liabilities
Accounts payable	[1]	3,281	2,899
Accrued expenses and other current liabilities		4,141	4,374
Current portion of long-term debt, financing and capital lease obligations		5,036	4,690
Total Current Liabilities		12,458	11,963
Long-term debt, financing and capital lease obligations		35,878	29,268
Deferred tax liabilities		14,416	13,959
Note due to consolidated affiliate		0	0
Other liabilities		3,563	4,002
Due to consolidated affiliate		0	0
Total liabilities		66,315	59,192
Total Stockholders' Equity		18,808	19,783	21,710	25,312
Total Liabilities and Stockholders' equity		85,123	78,975
Consolidation, Eliminations [Member]
Current assets
Cash and cash equivalents		0	0	0	0
Short-term investments		0
Accounts and notes receivable, net		(86)	(114)
Device and accessory inventory		0	0
Prepaid expenses and other current assets		0	0
Total Current Assets		(86)	(114)
Investment in subsidiaries		(42,654)	(42,912)
Property, plant and equipment, net		0	0
Due from consolidated affiliate		(13,057)	(19,568)
Note receivable from consolidated affiliate		(10,969)	(10,622)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill		0	0
FCC licenses and other		0	0
Definite-lived intangible assets, net		0	0
Other assets		0	(1,019)
Total assets		(66,766)	(74,235)
Current liabilities
Accounts payable		0	0
Accrued expenses and other current liabilities		(86)	(114)
Current portion of long-term debt, financing and capital lease obligations		0	0
Total Current Liabilities		(86)	(114)
Long-term debt, financing and capital lease obligations		0	(1,019)
Deferred tax liabilities		0	0
Note due to consolidated affiliate		(10,969)	(10,622)
Other liabilities		0	0
Due to consolidated affiliate		(13,057)	(19,568)
Total liabilities		(24,112)	(31,323)
Total Stockholders' Equity		(42,654)	(42,912)
Total Liabilities and Stockholders' equity		(66,766)	(74,235)
Parent [Member]
Current assets
Cash and cash equivalents		0	0	0	0
Short-term investments		0
Accounts and notes receivable, net		86	87
Device and accessory inventory		0	0
Prepaid expenses and other current assets		0	0
Total Current Assets		86	87
Investment in subsidiaries		18,800	19,783
Property, plant and equipment, net		0	0
Due from consolidated affiliate		25	50
Note receivable from consolidated affiliate		10,394	10,377
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill		0	0
FCC licenses and other		0	0
Definite-lived intangible assets, net		0	0
Other assets		0	0
Total assets		29,305	30,297
Current liabilities
Accounts payable		0	0
Accrued expenses and other current liabilities		103	137
Current portion of long-term debt, financing and capital lease obligations		0	0
Total Current Liabilities		103	137
Long-term debt, financing and capital lease obligations		10,394	10,377
Deferred tax liabilities		0	0
Note due to consolidated affiliate		0	0
Other liabilities		0	0
Due to consolidated affiliate		0	0
Total liabilities		10,497	10,514
Total Stockholders' Equity		18,808	19,783
Total Liabilities and Stockholders' equity		29,305	30,297
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents		2,461	2,154	3,492	4,125
Short-term investments		5,444
Accounts and notes receivable, net		1	27
Device and accessory inventory		0	0
Prepaid expenses and other current assets		11	12
Total Current Assets		7,917	2,193
Investment in subsidiaries		23,854	23,129
Property, plant and equipment, net		0	0
Due from consolidated affiliate		13,032	19,518
Note receivable from consolidated affiliate		575	245
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill		0	0
FCC licenses and other		0	0
Definite-lived intangible assets, net		0	0
Other assets		134	1,127
Total assets		45,512	46,212
Current liabilities
Accounts payable		0	0
Accrued expenses and other current liabilities		478	531
Current portion of long-term debt, financing and capital lease obligations		1,356	3,065
Total Current Liabilities		1,834	3,596
Long-term debt, financing and capital lease obligations		13,647	11,495
Deferred tax liabilities		0	0
Note due to consolidated affiliate		10,394	10,377
Other liabilities		837	961
Due to consolidated affiliate		0	0
Total liabilities		26,712	26,429
Total Stockholders' Equity		18,800	19,783
Total Liabilities and Stockholders' equity		45,512	46,212
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents		409	487	$ 518	$ 845
Short-term investments		0
Accounts and notes receivable, net		4,137	1,099
Device and accessory inventory		1,064	1,173
Prepaid expenses and other current assets		590	1,908
Total Current Assets		6,200	4,667
Investment in subsidiaries		0	0
Property, plant and equipment, net		19,209	20,297
Due from consolidated affiliate		0	0
Note receivable from consolidated affiliate		0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill		6,579	6,575
FCC licenses and other		40,585	40,073
Definite-lived intangible assets, net		3,320	4,469
Other assets		1,179	620
Total assets		77,072	76,701
Current liabilities
Accounts payable		3,281	2,899
Accrued expenses and other current liabilities		3,646	3,820
Current portion of long-term debt, financing and capital lease obligations		3,680	1,625
Total Current Liabilities		10,607	8,344
Long-term debt, financing and capital lease obligations		11,837	8,415
Deferred tax liabilities		14,416	13,959
Note due to consolidated affiliate		575	245
Other liabilities		2,726	3,041
Due to consolidated affiliate		13,057	19,568
Total liabilities		53,218	53,572
Total Stockholders' Equity		23,854	23,129
Total Liabilities and Stockholders' equity		$ 77,072	$ 76,701

[1] Includes liabilities in the amounts of $69 million and $66 million as of March 31, 2017 and 2016, respectively, for payments issued in excess of associated bank balances but not yet presented for collection.